1. Field
Example embodiments relate to methods for forming banks for retaining liquids and other flowable materials and organic thin film transistors including such banks. More specifically, example embodiments relate to methods for forming banks during the fabrication of organic electronic devices by utilizing a printing technique wherein a mixture of a water-soluble polymer containing a UV curing agent and a water-soluble fluorine compound is used to perform the formation and surface treatment of banks substantially simultaneously, and organic thin film transistors comprising such banks.
2. Description of Related Art
In recent years, a variety of polymeric materials have been investigated for their potential as novel electrical and electronic materials suitable for a wide variety of applications, e.g., functional electronic and optical devices. Polymeric materials may provide one or more advantages over previous materials including, for example, the relative ease with which they can be molded into fibers and films, improved flexibility, increased conductivity and reduced production costs. Research relating to electrically conductive polymers and their use in fabricating semiconductor active regions for organic thin film transistors has been ongoing for at least about 25 years.
Organic thin film transistors can be fabricated using relatively simple processes, such as printing, at relatively low cost. In addition, advantages associated with organic thin film transistors include relatively simple processes and their generally good compatibility with flexible substrates. In light of these advantages, a number of studies on organic thin film transistors are now ongoing around the world. Indeed, it is anticipated that organic thin film transistors will be particularly be useful in fabricating driving devices for active displays and in fabricating plastic chips that may, in turn, be incorporated into smart cards and/or inventory tags, for example RFID products.
However, the use of liquid or other flowable materials for forming and/or filling thin film patterns during the fabrication of organic electronic devices, such as display devices (e.g., electroluminescence (EL) devices and light-emitting diodes (LEDs)), in combination with conventional printing techniques can result in containment failures. For example, the liquid material(s) may overflow the bank and spread into the pixel regions of adjacent organic electronic devices, thereby degrading the properties of the affected electronic devices. For example, when a photoresist composition is used to form banks using an organic solvent in the fabrication of a bottom contact type or top gate type organic thin film transistor, overflow of the organic solvent can compromise the dielectric performance of adjacent organic insulating films, thereby potentially degrading the performance of the resulting organic thin film transistor.
As used herein, the term “bank” should be understood as referring to retaining structures, isolation structures, dams or partition members, i.e., structures configured to divide adjacent regions and suppress or prevent cross-talk between adjacent devices and/or to define enclosed regions that can subsequently be filled with a liquid or other flowable composition, for example, a suitable ink, to define discrete functional zones or regions on the surface of the device and improve the uniformity of the resulting device structure(s).
Many methods have been utilized in efforts to address the processing issues associated with the conventional formation and utilization of such banks. One such effort resulted in a method for forming banks comprising forming a polyimide layer, forming a photoresist layer on the polyimide layer, baking the layers, exposing the baked layers to a pattern of UV radiation during a photolithographic exposure process, developing the exposed photoresist layer to from a photoresist pattern and etching the exposed regions of the polyimide layer. This method also provided for post-etch surface treatment of the banks to alter the contact angle between the banks and the substrate on which they were formed. Another effort resulted in a method for forming banks comprising the steps of forming a layer of a polymer compound on a substrate, stamping the polymer layer, and baking the stamped layer. This method also provided for a surface treatment of the banks with plasma to modify the initial structure.
These conventional methods, however, remain generally unsuited for fabrication processes that include bottom gate type insulating films, which are general structures of display arrays that are, in turn, used to fabricate organic devices. In the fabrication of such devices, the organic devices are exposed to organic solvents and may be degraded as a result of this exposure. In particular, the solvent(s) and/or solvent systems present in the compositions utilized for forming the banks, for example, the photoresist solvent(s), developing solvents and photoresist stripping compositions can degrade the underlying and/or previously patterned organic materials which, in turn, can degrade the yield, performance and/or reliability of the resulting devices.